1. Field of the Invention:
This invention relates to quality testing apparatus for vacuum packaged products and, more particularly, to apparatus for testing the quality of packaging of vacuum packaged products by applying a stress to the package.
2. Description of the Prior Art:
Various types of pre-cooked meat products, such as bacon, wieners, and luncheon meats, are vacuum packaged in flexible plastic packages. The flexible package is theoretically sealed tightly so as to preclude the entrance into the package of ambient air pressure. As long as the package is free from holes and is sealed properly, ordinary refrigeration of the meat product and/or products, such as in stores, will prevent spoilage of the meat. However, if the package is not sealed properly, or if a pin hole leak develops in the package, the vacuum is lost and ambient air pressure is allowed to enter the package and spoilage of the meat results. A substantial percentage of packages are "leakers" as the result of such deficient packages. At the present time, and under prior art methods, there is no way to detect such leakers unless there is a noticeable defect in the package. The term "noticeable" is used to mean a hole or defect in the seal of a package which is large enough to admit sufficient air in the fifteen to sixty seconds between packaging and boxing to cause separation of the packaging film from the contents which can be detected by the naked eye. Unless a package defect is in a noticeable place or is rather large, the defect will probably not be detected and such leaker packages will be shipped out of the processing plant and to the ultimate point of distribution, such as a retail store.
Depending on the size or extent of the leak or defect in the package, spoliation will occur over a period of time. The length of time of course depends on the extent of the defect in the package. Regardless, any leaker will result in the spoiling of the meat product prior to the normal or expected shelf life of a well-sealed package.
While there are detection apparatus for determining surface leakage, such apparatus are limited in their scope to determining only the fluid tightness of a surface by vacuum methods. That is, a vacuum suction head of some kind is applied to the surface to be detected, and by pulling a vacuum on the surface, any leakage through the surface, for example through a sealed hole, from a rivet, bolt, or the like, may be detected by monitoring the vacuum pressure. Such apparatus is disclosed in U.S. Pat. No. 3,524,342, dated Aug. 18, 1970.
Similar apparatus is disclosed in U.S. Pat. No. 3,501,945, dated Mar. 24, 1970. The apparatus disclosed in the patent is directed to testing linings of closures, such as sealing rings, by applying a vacuum within the area of the sealing ring against a liner. If the sealing ring is defective, a flow of air will move through the sealing ring into the vacuum tester and will be detected thereby.
The types of apparatus disclosed in the two referenced patents are typical of the prior art, but are limited in their scope with respect to the detection of sealing defects or pin holes such as in vacuum packaged meat products. Accordingly, apparatus such as disclosed in the referenced patents is not applicable to solve the problems of the meat packing industry.
The prior art also includes apparatus such as disclosed in U.S. Pat. No. 3,117,441, dated Jan. 14, 1964. The apparatus described in this patent is for testing the quality of packaging of vacuum packaged products by submitting the package to a vacuum environment in a vacuum chamber. The pressure within the chamber is first decreased below that of the vacuum package to distend the package and is then increased. The pressure within the chamber is determined after the package has returned to a predetermined amount of distention. The chamber pressure is then compared to a predetermined value which indicates the condition of the package. The apparatus is rather time consuming to use, due to the many steps included in the testing process. The chamber is first opened, a package is inserted, and the chamber is then closed, sealed, and evacuated. The pressure within the chamber is decreased until the package has reached a given size, and the chamber pressure is then increased to atmospheric. The chamber is then opened, the package is removed and another package is inserted. The multiplicity of steps and the timing make the apparatus useful primarily for statistical quality control or for relatively slow production lines.